1. Field of the Invention
The present invention generally relates to a navigation system, and more particularly to an objective position information supplying method in a navigation system, which can supply various information as for an objective position to a driver, on the basis of the positional relationship between the detected self vehicle position and the objective position such as a destination and a passing position on the way to the destination.
2. Description of the Related Art
According to a navigation system, especially to an on-vehicle type navigation system, various information is supplied to a driver on the basis of the self vehicle position which is measured in a self sustained manner on the basis of the information from various sensors such as an earth magnetism sensor, an angular speed sensor and a travel distance sensor etc. which are mounted on a vehicle, or on the basis of the self vehicle position measured by use of the GPS (Global Positioning System).
As one of the supplies of this information, there is a supply of the information as for a scheduled passing position on a middle route to a scheduled arrival position from a starting position.
By this, the user sets a plurality of scheduled passing positions between a starting position 111 and a scheduled arrival position 115 in advance before starting as shown in FIG. 8A (in FIG. 8A, there are set 3 scheduled passing positions 112 to 114), and starts from the starting position 111. Then, on the route to the scheduled arrival position on a plurality of roads 107, when it is approaching to each of the scheduled passing positions or the scheduled arrival position (hereinbelow, these are referred to as objective positions all together), the fact that it is approaching is informed to the driver by an audio voice or a display. By this, the driver recognizes that it is advancing to the scheduled arrival position on a correct route.
In case of informing by use of the audio voice, for example, when it is approaching to the scheduled passing position A 112 as shown in FIG. 8A, it is informed to the driver as "we are soon at the scheduled passing position A 112".
Nextly, it is explained as for the method of judging whether or not it is approaching to the objective position in the above explained objective position information supplying method, by use of FIG. 8B.
In the above explained objective position information supplying method, there is provided a detection boundary line 106 connecting points which have equal distances to each other from an objective position 100 with a center located at the objective position 100 as shown in FIG. 8B. Since these points having the equal distances from the objective position 100 are connected to each other, this detection boundary line becomes a circle as a result. The radius thereof is set for each objective position in accordance with the characteristics of each objective position such as a relationship with the roads at its peripheral.
Then, when it is detected that the self vehicle arrives at the position indicated by a self vehicle position mark 101 in FIG. 8B, i.e., when the self vehicle position and the detection boundary line 106 are coincident to each other, it is informed to the driver that it is approaching to the objective position 100 by the above mentioned method.
According to this method, there is such an advantage that it is possible to judge whether or not the self vehicle is approaching to the objective position by use of a simple program.
In addition, according to the above explained method, the supply of the information to the driver is performed only once when the self vehicle position and the detection boundary line 106 are coincident to each other. The information as for the objective position 100 is not supplied after the self vehicle has advanced to the inside of the detection boundary line 106 (when the position of the self vehicle becomes the position indicated by a self vehicle position mark 101').
On the other hand, when the position of the self vehicle coincides with the detection boundary line 106 at the time of advancing to the outside of the detection boundary line 106 from the inside of the detection boundary line 106, the information as for the objective position 100 is not supplied.
However, according to the objective position approaching judgement method in the above mentioned objective position information supplying method, the detection boundary line is a circle, and the information as for the objective position is supplied to the driver only once when the detection boundary line and the self vehicle position are coincident to each other at the time of advancing to the inside of the detection boundary line. Thus, according to the study and research conducted by the inventor of the present application, there are various problems in this method as following.
With reference to FIGS. 9A, 9B and 9C, some examples of the problems found by the inventor of the present application are explained hereinbelow.
Firstly, as shown in FIG. 9A, in case that a plurality of roads exist at the inside of the detection boundary line 106, when the self vehicle arrives at the position indicated by a self vehicle position mark 102, the information indicating that it is approaching to the objective position 100 is supplied in the same manner as in the case where the self vehicle arrives at the position indicated by the self vehicle position mark 101. Then, the driver, who is located at the position of the self vehicle position mark 102, erroneously recognizes that it would arrive at the objective position 100 if it advances with maintaining the advance direction of the self vehicle, so that it advances with maintaining the direction as it is, and it goes away from the objective position 100 as a result.
On the other hand, as shown in FIG. 9B, in case that both of general roads 107 and a high way 108 are located at the inside of the detection boundary line 106, when the self vehicle arrives at the position of the self vehicle position mark 103 on the high way 108, the information indicating that it is approaching to the objective position 100 is supplied in the same manner as in the case where the self vehicle arrives at the position of the self vehicle position mark 104. Then, such a case is raised that the driver, who is located at the position of the self vehicle position mark 103, does not use the interchange 109 by erroneous recognition, although he should in fact go out of the high way 108 at an interchange 109 and go toward the objective position 100 via a road 110.
Furthermore, as shown in FIG. 9C, in case that the road to be used when it advances to the next objective position from the objective position 100 is located at the inside of the detection boundary line 106, the approaching information to the objective position 100 is supplied again at the position of the self vehicle mark 105 to the driver who has obtained the approaching information to the objective position 100 at the position of the self vehicle position mark 101 after it has passed through a crossing 116 via the objective position 100. Then, the driver erroneously recognizes that it would be approaching to the objective position 100 again although it is in fact advancing to the next objective position after the objective position 100.